A system of this general type has been disclosed in U.S. Pat. No. 3,771,382 granted to one of us, Richard Wilke, on Nov. 13, 1973. In that system the two bodies to be relatively displaced are a nut and a screw or spindle, the latter being formed with a thread in the shape of multi-turn helical grooving whereas the nut is provided with a similar groove forming an incomplete helical turn of the same pitch. The groove of the nut is complemented by a cylindrical insert in the nut body, provided with a diametrical recess, to form a closed guide path for an endless series of balls which (except during their passage through the recess of the insert) are received partly in the groove of the nut and partly in a confronting turn of the spindle grooving to act as spacers, the balls being freely movable along their guide path in either direction.
While the system of the prior patent is eminently suitable for spindles and nuts with threads of relatively short pitch compared to their diameter, threads of larger pitch and therefore larger helix angle can be accommodated only with difficulty since this necessitates an increase in the diameter of the insert and with it an enlargement of both the axial length and the thickness of the nut in order to preserve structural continuity.